An RF ID tag with a battery power supply or of an active type, which may be attached to a merchandise article or the like, or carried by a person, transmits an RF signal at a transmission frequency that carries an ID and other information related to the article or the person, so that the RF signal is received and the information is read out by a reader device. The read-out information is further processed by a computer or the like, so that the distribution of the article or the action of the person is monitored and managed. The active-type RF ID tag with battery power supply has a larger communication range than a passive-type RF ID tag that receives power from a reader/writer device in a contactless manner, and hence is practical in use. There is an improved active-type RF ID tag that responds only to a tag ID request transmitted by the reader/writer device.
A known information access system accesses information stored in an active-type contactless information storage device such as an RF ID tag. In such an information access system, a reader/writer device continually transmits an ID request signal at a first frequency and is continuously ready to receive an RF signal at a second frequency. The active-type contactless information storage device includes a receiver unit for sensing a carrier of an RF signal at the first frequency, and a transmitter unit for transmitting a response RF signal at the second frequency when the ID request signal is received. The receiver unit senses a carrier of an RF signal at the first frequency in carrier sensing periods occurring in a carrier sensing cycle. When the receiver unit detects a carrier of an RF signal at the first frequency in a particular carrier sensing period, the receiver unit receives the ID request signal, and the transmitter unit transmits a response RF signal at the second frequency carrying an ID. In the carrier sensing, the control unit causes the receiver unit to be in an active state and the transmitter unit to be in an inactive state in the particular carrier sensing periods. When the receiver unit attempts to sense a carrier of the RF signal at the first frequency in the particular carrier sensing period but detects no carrier, the control unit controls the receiver unit and the transmitter unit to maintain the inactive state during a non-carrier sensing period between the particular carrier sensing period for carrier sensing and the subsequent carrier sensing period for subsequent carrier sensing. Thus, the power consumption of the active-type contactless information storage device may be decreased.